PDA

View Full Version : re-foamed 4412 woofers



totaltech
01-28-2009, 03:25 PM
I have just had the woofers re-foamed (surrounds done) in my 4412 speakers. I re-installed the woofers, and gave them a go. to my surprise they sounded really bass shy!

I am using a PC2002m yamaha power amp - 235Wpc, so power is not a problem!

Do i need to break in the speakers?

Cheers

Rob

SEAWOLF97
01-28-2009, 03:29 PM
out of phase ?

totaltech
01-28-2009, 03:37 PM
g'Day Seawolf,
No i checked that. I wasnt expecting gut wrenching bass, but from the info I have read on here the bass should be pretty decent!

totaltech
01-28-2009, 04:01 PM
BTW SEAWOLF I was flicking through threads and saw your speaker safari one! Most entertaining!!!!!

I ex's partner works at out local tip, thats where I got the 4412's from! Grouse nick apart from mounting holes in the cabinet from brackets, and shot surrounds in the woofers.

Two days before that got 2 Yamaha amps a pc2002m and a pc2002! Its amazing some of the stuff that some people throw out!

SEAWOLF97
01-28-2009, 04:53 PM
Its amazing some of the stuff that some people throw out!

sure is ....:D

did you check correct polarity when wiring them back in after refoam and polarity from the amp ?

I had some 4412s ...they have plenty of bass

Oz ? may be down that way this Aug...30 days in VN then a week in Sydney.

totaltech
01-28-2009, 05:43 PM
I have found JBL compression drivers (2420's) home theater amps pc's good furniture you name it! The amps and speakers are the best find to date and zero cost! :D
VN? Victoria? I live 25kms NW of melb airport.

mech986
01-28-2009, 06:08 PM
Hello TT,

welcome to the LH forum!! Hope you have a great time here. There are quite a few members from down under so here's to you meeting up with them.

The 4412 is definitely not bass shy so I second the recommendation of checking and double checking the phasing and polarity of each component that was possibly affected - the wiring at the amps and at the speakers, the wiring from the speaker terminals to the crossovers and then crossovers to the drivers. Double check the absolute polarity of the drivers themselves - a C or D cell voltage touched to the woofer terminals should be consistent for both speakers.

Here's JBL Professional's white paper on the subject:

http://www.jblpro.com/catalog/support/getfile.aspx?docid=241&doctype=3

Interestingly 4412's are negative going while the 4412A's are positive.

IF you think its all ok and the bass still is thin, reverse one set of wires at one speaker only and see if the bass gets even worse or gets better. If better, there IS a polarity inversion either in the woofer itself or one of the cables or maybe even before the amp. (Check to see if any of your amps have been worked on, maybe someone miswired them too).

If worse, then the problem lies with the woofers themselves. Check to see if there is any hangup with the voice coils. Check against other photos about the size of the roll used on the replacement surrounds. Sometimes the rolls are narrow by design and need to be pretty exact for proper compliance and movement. If more generic rolled surrounds are used, these typically are wider and somewhat stiffer, impeding full cone movement as JBL intended.

BTW, the OEM placement of the surrounds for the 128H-1 is on the back of the cone, not the front. Improper placement of the surround will lead to an asymmetric static position of coil to gap and produce distortion and Xmax changes beyond design parameters.

Welcome, and hope this helps.

BTW, great score on those Yamaha PC2002M and PC2002 amps - quite a few of us know them well. When you have a chance, snap a few pictures of them and the speakers to let us see what you have. Be sure to resize the pics to 800 x 600 so they post ok here.

Regards,

Bart

SEAWOLF97
01-28-2009, 06:12 PM
I
VN? Victoria? VietNam

pierce
05-08-2009, 08:36 PM
what model woofer is in your 4412 that you refoamed ?

I -thought- the 4412(A) used the 2214H, but I've been told its something else...

edit: ok, I think I figured out that at least some of these used 128H(-1? -2?) ... did all the 4412's use 128H-* speakers right up to the early 2000s?!?

and whats the difference, I can't find any data on the 128H-*, is that an alnico speaker rather than a ferrite ?

BMWCCA
05-08-2009, 11:21 PM
and whats the difference, I can't find any data on the 128H-*, is that an alnico speaker rather than a ferrite ?All 4412/A use 128H-1. As far as I know, the "H" in a JBL speaker means ferrite. The 128H was used in the 4411, L112, L150/A, etc. Those had white cones. The H-1 is essentially the same with a black cone. Fine 12" woofer. Plenty of bass!

Doctor_Electron
05-10-2009, 10:22 PM
About ten years ago I asked the owner of an authorized JBL Pro service shop about repairing the failing surrounds on my 4400s' woofers. He presented a convincing argument against refoaming vs. reconing, as using non-JBL materials would make it impossible for such a repaired unit to meet original specs, which BTW I believe would be guaranteed for 90 days by JBL if done properly.

Well, as things later turned out I wound up working there. Eventually he refoamed the woofers as a "favor". (The real JBL kits were/are quite pricey and my financial situation demanded that I not "owe my soul to the company store").

The resultant sound of the 4410s' low end is now markedly distorted, which was never the case before the refoam, even with the holes and cracks that had appeared in the old surrounds after 15 years of non-abusive use .

I recently acquired a pair of 4412's from a "DJ", with woofers freshly reconed by a JBL shop. My decision to buy this pair and the price I paid was based on their
woofers having been recently reconed by JBL.

You might get lucky with a refoam, you might not. I did not, and because of that experience would not re-foam unless it's done on a less expensive system than 4410's, 4412's, or better... unless I had no expectation of their performance after a refoam.

On the other hand, if the cost of refoaming is cheap enough, you can always have them reconed later if you're not satisfied with the results of the refoam.

BTW, it's good that you have the power of the Yamaha to drive the 4412's, as in my experience they need lots of it to provide the performance that they are capable of.

BMWCCA
05-11-2009, 11:07 AM
The resultant sound of the 4410s' low end is now markedly distorted, which was never the case before the refoam
"Distorted" could be a bad re-foam or poor alignment; you name it. Empirical evidence without control is not definitive. So I'll add mine. When I got my L80Ts ($50 on Craig's List), one 127H-1 was missing all it's surround and the other was still intact. I re-foamed the former using Rick Cobb kits and played it next to the latter. Granted I'd performed the Gordon W mods to the port tube (adding 1.5") and adding about 4" of insulation to the top of the cabinet, but playing them side-by-side if anything assured me the refoam was done correctly and resulting mods made for a less-hollow "boxy" sound with better kick and extension to the bass. I can't measure to qualify the extension but the experience for me was an improvement in the re-surrounded, modded system. Foam isn't rocket science. Assuming the original durometer of decades-old foam may be difficult, making reproducing parts a bit of a guess, but then modern manufacturing methods might also alter the specs in foam supplied to JBL for their cone kits, too. Certain chemicals used in the '70s may no longer be allowed today and nearly anything manufactured in the petro-chemical industry has tighter standards for aromatic hydrocarbons and volatile organic compounds (hexane, cycloalkane and aromatic compounds, such as benzene, toluene and xylenes) these days and methods of manufacturing have probably been altered to comply. But then age affects such compounds, too. And who knows how long that re-cone kit has been sitting on that Calfornia warehouse shelf?

I'm not disputing the dogma that using a JBL re-cone kit is always the best way to re-surround a vintage JBL. I do find it difficult to believe that good results that might possibly restore a driver to original specs cannot be had by correct installation of carefully selected surround material on the original cone. Plus, I'm a cheapskate with champagne taste on a beer budget. And currently paying for two college tuitions with a third in the near future, so even beer is off the list! Maybe that's just wishful thinking? :dont-know

pierce
05-11-2009, 11:13 AM
...When I got my L80Ts ... I'd performed the Gordon W mods to the port tube (adding 1.5") and adding about 4" of insulation to the top of the cabinet...

(...not meaning to hijack the thread or anything, heh...)

I'm real interested in this? Is there a reference URL to this? Is there an equivalent mod for the L100T ? :deal: